Generally the invention relates to the field of controlling computer tape drive devices which interface with a computer through standard floppy controller circuitry. Specifically, the invention focuses on techniques to specifically activate and deactivate the tape drive without any need for additional circuitry or revision to existing floppy controller designs.
Since the advent of computers, the need to store information has grown dramatically. This information storage is frequently accomplished through devices which interconnect and act relatively independently in response to signals received from the main data processing functions of the computer. These devices, known as peripheral devices, act to retrieve data from the main computer memory and then to store such data on a separate media associated with the peripheral device.
One of the aspects of typical memory devices in computer systems is their volatility--they can unintentionally lose their contents occasionally. To overcome this undesirable aspect, backup devices have evolved. Such devices serve the simple function of separately storing large amounts of data on relatively nonvolatile media. In the field of these specialized devices the use of magnetic tape media has greatly eclipsed all other types of storage media. As a result of this demand, specialized peripheral computer tape drives have been developed. These tape drives have been especially designed to integrate into the existing electrical and mechanical designs of computer systems. Since the development of electrical and mechanical computer designs preceded the development of the computer tape drives, the design of tape drives has been constrained for practical and commercial reasons.
The significance of these constraints is perhaps underscored through analogy with the development of computers themselves. As may be recalled, computers were initially developed with a variety of architectures and configurations. Over time, however, the simple market dominance of one or two companies--most notably International Business Machines Corporation--resulted in standardization of many attributes of the computers. In essence, those companies that continued to make computers which did not function in a fashion consistent with the major portion of the market were often doomed to commercial failure. Thus it became very commercially significant to be able to claim that your computers were "IBM compatible" or functioned well with other significant segments of the market.
With respect to the development of peripheral devices, it similarly has become a standard that many of these devices function and integrate with the computer in a standardized fashion. This has evolved into a configuration whereby the drive device communicates and is controlled by a a floppy controller. As the name implies this controller was originally designed to control the then-predominant storage drive device--a floppy drive. Since computer tape drives became popular only after many computers utilizing floppy controllers were already in existence, an important commercial attribute which was well recognized by those skilled in the art was that such tape drives should integrate with existing designs, that is they should use the floppy controller.
While challenges were presented in utilizing a controller not specifically designed for the tape drive device, these were eventually overcome. To promote standardization, the fashion in which computer tape drives communicate and interact with the floppy controller has even evolved into a unique set of standards. These standards have been developed by a consortium of those involved in the computer tape drive industry known as the Quarter Inch Cartridge Drives Standards, Inc. (QIC). Thus the standards have become known as QIC standards. While these standards have had a generally positive impact, as with any standard, they have also acted to limit the thinking of those skilled in the art. Rather than merely presenting a means within which to achieve an end, such standards have at times become the end in themselves.
As mentioned, the QIC standards address not only the actual function of tape drives but also how such drives interact with the floppy controller. For instance, since the techniques of transferring control of data are fundamentally different between tape drives and floppy drives, the QIC standards have established that one line, the step line (a line which was designed to move the head on a floppy drive in a step-wise fashion) is used as a serial data transfer line for tape drive devices. An important attribute regarding how computer tape drives function through use of a floppy controller is the manner in which the floppy controller selectively activates and deactivates the particular tape drive. As to this function, the majority of tape drives and floppy controllers function similarly--each uses a "select line". This select line is actually a separate line which when activated "turns on" the device (whether floppy drive or other devices) to which it is connected, and when deactivated "turns off" that drive. One of the limitations of this configuration is the need for a separate line for each drive. Since floppy controllers exist in many instances with only two select lines, the number of drives can be likewise limited.
Several solutions to this well recognized limitation have been developed. By far the most prevalent commercially is the solution which utilizes a separate circuitry card to expand the number of select lines possible. While this solution is effective, it has two important commercial drawbacks. First, it requires additional hardware and thus additional cost. Second, it significantly complicates the difficulty of installing a tape drive. Recently, a system which apparently has not been publicly disclosed as such, appears to have been developed which utilizes a particular command sequence within the QIC standard command structure. These commands are then transmitted across the step line to activate the tape drive. While this system does eliminate some aspects of the need for select lines, the design of it is such that limitations and potential conflicts exist for specific drive configurations.
While each of the above limitations have been recognized, a solution to such problems has not, prior to the present invention, been available. Certainly the long felt need existed and as the present invention shows, the implementing arts and elements had been long available. Perhaps due to the commercial impact of standardization, those skilled in the art simply failed to recognize that a solution could be had without violating such standards. Surprisingly, the standards and the solutions proposed by those skilled in the art explicitly taught away from the direction from which the present inventors have approached the problem. Rather than adding hardware needing separate installation efforts or working within the confines of a standardized command structure, the inventors recognized that a new structure could be implemented and still meet the true purpose of standardization.
In addition to the problems posed with respect to initiating operation of a computer tape drive, there are problems with respect to disengaging the tape drive as well. Again, the invention poses similar solutions to such limitations. The invention also, however, goes beyond that and addresses potential conflict problems as well.